The definition of fine patterns in an aluminum film supported on a substrate is recognized as an important step in the production of silicon integrated circuit technology. It is likewise well recognized that the reproducible etching of aluminum is difficult to achieve.
Traditionally, aluminum patterns are defined by etching utilizing a photoresist as an etch mask. Wet chemical etching utilizing acids has been the predominate etching method in past years. This method is recognized as having a number of disadvantages.
Wet chemical etching of aluminum is completely isotropic, i.e., the etch proceeds in all directions at the same rate. There is also frequent loss of adhesion between portions of the photoresist and the aluminum. The former produces a reduction in line width in the aluminum with respect to the mask, and the latter causes loss of resolution in those areas where the photoresist has separated from the aluminum. Wet chemical etching is further disadvantageous in that it is expensive due to the large amount of high purity chemicals which are required. There is also the inherent hazard of handling the acid etchants and the problem of how to safely dispose of them after use.
As a result of the above disadvantages of wet chemical etching, the semiconductor industry is turning to dry etching methods, i.e., plasma etching or reactive sputter etching. In these methods, etching is carried out wholly or partially by reactive species generated in a plasma or gas discharge. The reactive species react with the aluminum to form one or more volative compounds which are pumped away with the unreacted gas by a vacuum pump. Such dry etching techniques are free from the aforementioned disadvantages involving the use, handling and disposal of highly acidic etchants. Further, such dry etching techniques are generally highly anisotropic, i.e., unidirectional, thereby producing superior line definition. However, those skilled in the art recognize that such techniques also have certain disadvantages, predominately associated with the extreme reactivity of the reactive species which etch the aluminum. The present invention is directed to alleviating the problems caused by the extreme reactivity of the reactive species.